1. Field of the Invention
The invention relates to a silo for bulk material with at least one pneumatic conveyor chute extending at least partially in a de-aerated space formed by a cover, toward an outlet opening. More particularly, the invention relates to such a pneumatic conveyor chute.
2. Prior Art
It is known to place pneumatic conveyor chutes upon the silo base which slopes gently toward the outlet opening, which conveyor chutes are to convey the material made flowable by finely distributed air supplied toward the outlet opening. It became manifest that openly placed pneumatic conveyor chutes can assure a uniform drain of the material over relatively short distances only, since primarily the material closest to the outlet opening is affected while for more distant material the loosening presure is not sufficient to overcome the resistances to the flow on the way to the outlet opening. By the employment of one or more expansion chambers (German Federal Republic Patent DE-PS 1,129,892) whose openings are distributed over the silo base in such a way that sufficiently short supply paths are produced, a uniform silo drain can be achieved. They are, however, relatively expensive because their height must be such that above the material level formed in these paths there remains a de-aerating space free of material. On the other hand, air conveyor chutes above which is provided at a small height (German Federal Republic Patent DE-PS 1,129,892, FIG. 8) a cover for the protection from the effect of the material load are only of limited success.
This applies also to closed conveyor chutes whose cover is perforated in places for the access of the material (German Federal Republic Application DE-OS 7 44 853). The reason is that they become completely filled with the material to be conveyed, in which process the resistance to flow and the pressure both rise, due to the growing air volume and the thereby increased velocity of flow toward the outlet opening, whereby the conveyance and the supply of further loosening air are checked.